Semiconductor devices, in particular memory devices with an integrated memory chip, but also unpackaged semiconductor chips, are conventionally attached on electronic printed circuit boards (PCBs), by being soldered onto the electronic printed circuit boards. Printed circuit boards with a number of memory devices are used for example as memory modules. The semiconductor chips of the semiconductor devices are connected to the chip package for instance by bonding wires. The chip package has contact terminals, which are soldered onto corresponding contact terminals of the electronic printed circuit board.
Integrated semiconductor circuits contain a plurality of dopant regions, which are thermally created by diffusion processes. After completion of the integrated semiconductor circuit, during the further processing of the chip and during later operation, the dopant profiles of the dopant regions are intended to remain unchanged. If the contact terminals of a memory device are soldered onto the printed circuit board, the heated solder contacts lead to the memory chip itself being heated up again. As a result, the dopant profiles can change again; for example, buried straps which establish the electrical connection between selection transistors and trench capacitors of a memory cell array can become high-impedance. Small changes of the dopant profiles also allow leakage mechanisms of integrated memory cells to come into being, with the effect of reducing the storage time (retention behavior). Dopant profiles of other doped regions may also be distorted by the temperature increase brought about by the soldering-on process. The thermal budget that must not be exceeded to maintain the spatial form of the dopant profiles may be exceeded, at least locally, as a result of the soldering process. Even if only a limited amount of heat is supplied during the soldering, a residual risk of undesired dopant diffusion in the semiconductor chip nevertheless remains.
Furthermore, the use of solder pastes leads to disposal problems if they contain lead. Leadfree solder pastes, on the other hand, are nowadays only suitable to a limited extent for wetting the contact terminals to be contacted of chip packages and electronic printed circuit boards.